Re: draft-ietf-impp-pres-01

Dave,

You've expressed part of what I was trying to say in a much clearer way.
Let me re-explain the rest:

I was talking about the difference between context-based uniqueness (what I
called the relaxed one - where the context is the watcher/presentity pair)
and self-identified (which I think we called "globally unique").

In addition to the trade-offs mentioned below, there is also the issue of
generating the extra bits for a self-identified unique identifier, as well
as the burden of ensuring that this identifier is globally unique.
Whoever/whatever is generating those bits must have the means to ensure
self-identified uniqueness.

Instead of arguing how much that burden is, I was wondering whether there
are any reasons to go with a globally unique one, keeping in mind, that
there is nothing that prevents us from using a globally unique identifies,
in a specific To/From context.  It would still be unique.

Thanos
---
Thanos Diacakis
Openwave Systems
[email protected]
+1-303 385 6705

----- Original Message -----
From: "Dave Crocker" <[email protected]>
To: "Thanos Diacakis" <[email protected]>
Cc: "Peterson, Jon" <[email protected]>; "John Ramsdell"
<[email protected]>; <[email protected]>
Sent: Tuesday, January 14, 2003 12:56 PM
Subject: Re: draft-ietf-impp-pres-01


> Thanos,
>
> Tuesday, January 14, 2003, 9:28:14 AM, you wrote:
> Thanos> I don't see how the multiple subscriptions has anything to do with
this.
> Thanos> Multiple subscriptions work even if you relax the uniqueness reqt:
>
> An identifier is useless if it is not unique.  So there is no "relaxing"
of
> the uniqueness requirement.
>
> However there certainly are legitimate choices about the way to ensure the
> uniqueness.  These involve tradeoffs in the scope of utility for the
> identifier and the bit-efficiency needed to encode it.
>
> The simple choice is between what I will call self-identified uniqueness,
> versus context-based uniqueness. The former contains all of the data
> necessary to ensure uniqueness, within the identifier itself. Email
> addresses are an example.  So are URIs.
>
> The latter relies on some larger context to ensure uniqueness. TCP port
> numbers are an example since they are relative to the IP address. For that
> matter, the definition of a TCP connection is an aggregation of such
> context, relying on IP address/port pairs from both connection
participants
> to define the unique connection identifier.
>
> The choice between self-defining and context-based identifiers is probably
> best made in terms of lifetime and encoding constraints.  If the
identifier
> is long-lived -- and especially if it might be used in other contexts --
> then it is better to make it self-defining.
>
> If it is essential to save bits, then context-based identifiers are
probably
> preferred.  However note that this establishes a critical dependency.  For
> example, the dependency that TCP connections have on the underlying IP
> address has constrained the ability to pursue some mechanisms that would
> help with multihoming and mobility.
>
>
> d/
> --
>  Dave <mailto:[email protected]>
>  Brandenburg InternetWorking <http://www.brandenburg.com>
>  t +1.408.246.8253; f +1.408.850.1850
>
>




  [reminder: [email protected] for non-technical discussions, please]